1. Field of the Invention
This invention relates to a method of producing an ion exchange membrane having grafted branches of acrylic acid and/or methacrylic acid on a polyethylene film. The invention is characterized by a method of producing an ion exchange membrane having low electrical resistance which comprises the steps of irradiating a polyethylene film not more than 150 .mu.m thick with ionizing radiation to give a total dose of 1-30 Mrads in vacuum or in an inert gas, reacting the film with a 15 to 50 wt% aqueous solution of acrylic acid and/or methacrylic acid at 15.degree. to 50.degree. C. to prepare a graft copolymer, and treating the graft copolymer with a 20 to 10 wt% aqueous solution of potassium hydroxide.
2. Description of the Prior Art
Ion exchange membranes are important as diaphragms indispensable to electrolysis and electrodialysis. Membranes made of sulfonated styrene-divinyl benzene or styrenebutadiene copolymer do not have adequate mechanical strength or chemical resistance and so they find use only in limited applications.
A method is known of producing an ion exchange membrane from a polyethylene base which is chemically very stable and is highly chemical resistant and which has incorporated therein electrolytic groups by graft copolymerizing acrylic acid and/or methacrylic acid onto polyethylene. But an ion exchange membrane produced by this method is not adequately low in electrical resistance primarily because polyethylene is so hydrophobic that electrolytic groups are not uniformly introduced throughout its thickness during manufacture using a conventional technique.
Therefore, the inventors of this invention made extensive and thorough studies on the reaction of graft copolymerizing acrylic acid and/or methacrylic acid onto polyethylene using ionizing radiation having high penetrating power, and have now sucessfully prepared an ion exchange membrane having very small electrical resistance by combining limited conditions selected for many steps.